This invention relates to an exhaust gas recirculating system wherein part of exhaust gases from an internal combustion engine is introduced back into a suction system of an engine to thereby lower the combustion temperature of the engine, thus reducing the amount of nitric oxides (which will be referred to simply as "NOx," hereinafter) contained in the exhaust gases, and more particularly to an alarm device for use in an exhaust gas recirculating system for detecting the abnormal recirculation of an exhaust gas recirculating flow.
Hitherto, an exhaust gas recirculating system has been proposed, in which part of exhaust gases from an internal combustion engine is introduced back into the engine to thereby reduce the amount of NOx contained in exhaust gases. It has been often experienced with this type of exhaust gas recirculating system that an exhaust gas control valve for controlling the recirculating flow rate of exhaust gases is damaged due to vibration or the like accruing from the travelling of a motor vehicle. As a result, the exhaust gas control valve will not operate in the normal condition so that an excessive amount of exhaust gases is fed into the engine, thus resulting in a lowered output or increase in the amount of hydrocarbons and carbon monoxide. In addition, it sometimes happens that a diaphragm in the exhaust gas control valve is broken, so that the control valve closes an exhaust gas recirculating passage, thus failing to feed exhaust gases into an engine, with the accompanying increase in the amount of NOx. Accordingly, it has long been desired to have an alarm device for notifying the abnormal recirculating condition of exhaust gases, thereby solving the aforesaid problems.
To meet such demand, there have been proposed an alarming device, by which to detect the stroke of an exhaust gas control valve in an exhaust gas recirculating system to warn of the abnormal recirculating condition of exhaust gases, or another alarm device by which to compare the pressure in a control pressure chamber in an exhaust gas control valve with a signal produced in a carburetor to thereby warn of the abnormal recirculating condition.
However, the alarm devices of this type are designed so as to directly detect the operating condition of an exhaust gas control valve, so that if a weld portion between a valve rod provided for a diaphragm and a valve portion in an exhaust gas control valve is ruptured or in case the valve rod causes troubles in its operation, there is a possibility of failing to detect the abnormal recirculating condition.